Integrated circuit devices are created by a multistep sequence of operations. A monocrystalline silicon wafer having a relatively large diameter, such as three or four inches, is used as the substrate. The wafer can undergo several steps of polycrystalline silicon deposition at elevated temperatures in a furnace. The polycrystalline silicon, commonly referred to as "poly", is deposited on the wafer from a gas passing over the wafer including silane (SiH.sub.4).
In the typical construction, an oxide layer will be formed on the silicon wafer prior to poly deposition and between other added layers of semi-conductor material. The oxide layers are substantially nonconductive and act as an insulator between the substrate and poly layer or between two poly layers.
To form holes at selected areas through the oxide layer to permit electrical communication between semi-conductor layers, the oxide layer is coated with a "photoresist" material. This photoresist material is responsive to light, and in particular ultraviolet light. A photomask is prepared from the original design for the integrated circuit which comprises a photographic negative having light transparent and opaque regions tracing the desired circuit design. The mask is placed over the photoresist and a light is shown through the photomask to initiate a chemical change in the portions of the photoresist under the transparent regions of the photomask. It is then possible to wash away either the portions of the photoresist exposed to light or that not exposed to light. Whichever technique is employed, the elimination of the photoresist in certain regions permits direct exposure of the underlying oxide layer. The underlying oxide layer may then be etched in these regions by etchant, such as acids. This provides exposure of the semiconductor region beneath the oxide at selected regions on the surface of the integrated circuit. A conductive metal may then be deposited on the surface with the metal flowing into electrical contact with the underlying semiconductor region. Similar procedures can be used to form selected holes or gaps in the semi-conductor layers to form discrete "islands" of semi-conductor material. A sequence of steps will build the semiconductor and oxide layers and interconducting metal conductors to form the complete integrated circuit chip.
In the past, the poly layer has been deposited on a substrate in a furnace heated above 800.degree. F. A silane rich gas is passed over the heated wafers in the furnace to deposit the poly layer. The wafers are mounted on a quartz boat and inserted into a quartz tube within the oven. Metal cannot be used in any area proximate the wafer as metal contaminants will diffuse into the wafer. However, the yield of operating integrated circuits from each circuit undergoing preparation is far less than 100%. With the cost of production, a need exists to improve the yield to reduce the final product cost.